PNNL

Abstract

Benzofluorene (C17H12) has been studied in argon matrices via Fourier transform infrared and UV-visible absorption spectroscopy and in the vapor phase by Fourier transform ion cyclotron resonance mass spectrometry. Analysis of the infrared absorption spectra of neutral and cationic 2,3-benzofluorene was supported by density functional theory calculations of the harmonic mode frequencies. Extensive time-dependent DFT calculations of the electronic vertical excitation energies at various levels of theory were performed to assign the observed electronic absorption bands of the neutral species. Although the observed low energy absorption bands are predicted well by theory, the higher energy bands have only been assigned tentatively. On the other hand, the observed electronic absorption bands for the parent, singly-dehydrogenated cationic and neutral species are in accord with the TDDFT results. The identification of certain fragmented species from electron impact/matrix optical experiments led to detailed studies of the dissociation pathways of the cation via Fourier transform-ion cyclotron mass spectrometry. Both hydrogen and acetylene loss pathways along various photodissociation routes have been identified. The possibility that the 2,3-benzofluorene cation contributes to the unidentified infrared (UIR) bands observed from interstellar space is discussed briefly.